Dryer seal



Oct. 1, 196

Filed Aug. 29, 1966 h '2 W 1H S. G. MASTERS ETAL DRYER SEAL 2 Sheets-Sheet 1 INA M0915 arm 5v can/ :57:25,

WILL/M0. mm,

Oct. 1, 1968 S. G. MASTERS ETAL 3,403,457

DRYER SEAL Filed Aug. 29, 1966 2 Sheets-Sheet 2 lA/VE/WU/PS 5 721 5 6 .M/lsms MAL/HM 0. W735,

United States Patent 3,403,457 DRYER SEAL Steven G. Masters and William D. Poats, Waynesboro,

Va., assignors to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Filed Aug. 29, 1966, Ser. No. 575,801 8 Claims. (Cl. 34242) ABSTRACT OF THE DISCLOSURE A conveyor dryer seal comprising a trough having a fiat bottom curving upwardly and extending across the width of the conveyor belt, and suspending means which allows movement of the trough towards and away from the belt while maintaining the fiat bottom of the trough parallel to the face of the belt. A preferred suspending means comprising two parallel rectangular members, one edge of each being hinged to one of the sides of the trough and the other edge being hinged to the dryer framework, is disclosed.

This invention relates to an improved continuous dryer for materials of small size laid down in a substantially continuous sheet on a moving belt, especially staple fibers and other fibrous materials. More particularly, the invention relates to an improved seal for such dryers.

In a conventional apparatus employed commercially for drying staple fibers, the fibers are deposited at one end of a continuous perforated belt which carries the fibers through an elongated drying zone in which heated, relatively dry air is passed vertically through the fibers and moving belt. The passage of the air through the belt is conveniently provided by using circulating fans to suck air from the space beneath the belt, creating a slight negative pressure under the belt. An exhaust means, which removes air from the dryer, contributes to this slight nega tive pressure to a greater extent than the circulating fans. An effort is usually made to keep the air above the belt. from the entrance to the exit of the dryer, at the same pressure as the air outside the dryer. In practice, however, fluctuations in pressure do occur between the interior and exterior of the dryer. When this happens, cool exterior air flows into the dryer or heated interior air flows out of the dryer above the belt at the entrance and at the exit, reducing the efficiency of the dryer.

Attempts to seal the entrance and exit of the dryer to eliminate loss of heat while still permitting passage of the staple fiber on the moving belt has met with a variety of problems. A particularly troublesome problem is the entanglement of masses of fibers in the form of clumps or ropes upon the seal itself, or near the seal as the result of its disturbing effect on the passage of the fibers, with subsequent release of the entangled fiber masses at random intervals. Staple fibers of most synthetic material, such as fibers of acrylonitrile polymer, become undesira'bly degraded and discolored when exposed to heat for prolonged periods; and the random release of degraded, entangled fiber masses therefore contaminates the product. Another problem is that gaps opening intermittently at the entrance and exit of the dryer as the result of inefiicient sealing permit passage of gusts of air, blowing quantities of stable fibers along the belt and over the side of the belt. This results not only in the loss of product, but also requires frequent cleaning of the equipment and nearby area.

An object of the present invention is the provision of a highly efiicient seal for conveyor belts carrying fibrous materials between zones having different gas pressures especially for sealing the entrances or exits of dryers employing moving conveyor belts.

3,403,457 Patented Oct. 1, 1968 In accordance with this invention an improvement is provided in an apparatus for drying fibrous materials. The apparatus generally comprises an elongated housing having an inlet and an outlet opening for the fibrous materials, a continuous perforated belt mounted therein for carrying the fibrous materials through the housing, means for introducing a gas into the housing, means for heating the gas; and means for passing the heated gas through the belt and removing the passed gas from the housing. The improvement comprises a novel seal in either the inlet or the outlet (or both) of the housing, the seal comprises a trough extending substantially across the width of the opening, the trough having enclosed ends parallel to the Sides of the belt, and a flat bottom curving upwardly to form curved front and rear sides perpendicular the sides of the belt. Connected to said trough are sus pending means for allowing the movement of the trough towards and away from the belt while simultaneously maintaining the flat bottom of the trough substantially parallel to the face of said belt.

A highly preferred suspending means structure comprises two parallel rectangular members of substantially equal size extending substantially across the width of the opening, one edge of each of the rectangular members being attached by hinges to one of the sides of the trough, the opposite parallel edge of each of the rectangular members being attached by hinges to the top of the housing, all of the hinges being parallel to the face of the belt, and perpendicular to the sides of the belt.

The invention will be better understood by reference to the attached drawings, in which,

FIGURE 1 is a schematic view of a dryer provided with the seals of the present invention at both the entrance and exit; with the near side of the dryer removed to reveal the interior;

FIGURE 2 is a transverse, cross-sectional view along the line AA of the dryer of FIGURE 1; and

FIGURE 3 is an isometric view of the seal at the entrance to the dryer, with a portion of the near wall of the dryer cut away and the dryer shown with the belt in motion and carrying a fibrous material.

Referring now to the figure-s, FIGURES 1 and 2 illustrate a dryer comprising a perforated conveyor belt 1 mounted to pass continuously in the direction shown by the arrows through the elongated housing 2 of the dryer. Side belt guards (not shown) similar to those disclosed in US. Patent No. 3,069,786 are employed in a preferred embodiment. Staple fibers or other materials to be dried are deposited onto the moving conveyor belt from chute 3 or other suitable feeding means. Air, or other gas suitable for drying, enters from inlet duct 4 in the space under the conveyor belt. Air under the belt is drawn at one side of the belt by circulating fans 5 through heating coils 6 to the space above the belt, from which the air passes downwardly through the perforated belt and the fibrous material carried thereon and returns to the space below the belt. The direction of air flow through the belt is shown by the arrows in FIGURE 2. Air is withdrawn from exhaust vent 7, located in the space beneath the belt at the entrance end of the dryer. The air is thus induced to follow a generally helical path from the exit to the entrance of the dryer. Curved baflies 8 encourage the circular motion of the air through the belt. The presence of an inlet duct as such may be eliminated if a sufliciently large quantity of air is otherwise available, e.g. through leakage of air into the housing.

Seals 9, provided at both the entrance to and the exit from the dryer, comprise suspended troughs 10 with closed ends 11. FIGURE 3 illustrates the seal at the entrance to the dryer in detail. Each trough has a flat bottom 12 curving upwardly to form front and rear sides 13 and 14, respectively, usually formed from a single sheet. An elongated hinge 15 attaches the top edge of the front side to rectangular supporting member 16, and elongated hinge 17 attaches the top edge of the rear side to rectangular supporting member 18, having the same size and shape as supporting 'member 16 and parallel to it. Supporting members 16 and 18 are hinged in turn to extensions of the housing outside vertical end walls 23 of the housing.

In FIGURE 1 the seals are shown in the lowest vertical position, just touching the belt. In FIGURE 3 the seal shown in FIGURE 1 is shown in a somewhat raised position, just permitting passage of the fibrous material 19 while preventing passage of air from the dryer to the outside. The seal may also be positioned so that its lowest vertical position is a predetermined distance from the belt (e.g., approximately the thickness of the fibrous material on the belt). This is less advantageous in that an opening between the seal and the belt exists when a lesser amount of material is on the belt (or when the belt is empty).

The trough is raised by means of cables 20, the length of which is adjusted by turning crank 21. The cable is preferably flexible and of adjustable length, so that it acts to hold the trough at the desired vertical distance from the belt on one side of lowest vertical position without preventing the trough from upward movement in response to larger than normal masses of material passing underneath it on the belt. The maximumlength of the cable can be chosen, if desired, so that the trough can not rest in its lowest position. In an alternate embodiment not shown, the cables 20 can be connected to opposite sides of the trough. When the cables are oppositely wound on crank 21 turning the crank clockwise shortens one cable and lengthens the other cable. Turning the crank counterclockwise has the reverse effect. In this manner, the trough can be moved vertically on either side of its lowest vertical position.

Strips 22 of flexible material are attached to the edges of the trough and supporting member and extend the edges of the seal to fit the walls of the housing with the minimum possible clearance. Such strips can also be employed as seals at other locations in the dryers e.g., at the lower edge of stitfeners mounted upon the lower side of the moving belt and forming a seal between the belt and T seal beneath the belt.

The trough and supporting members of the seal are conveniently constructed of metal, a suitable material being stainless steel. The strips of flexible material at the ends of the seal are conveniently formed from polytetrafluoroethylene film.

The hinged parallel rectangular supporting members in the seal provided by the present invention, when viewed from the side, form a parallelogram in which a portion of the dryer housing forms the top of the parallelogram and the top of the trough forms the bottom of the paralleogram. Vertical movement of the trough thus also shifts it laterally and changes the slope of the supporting members; but the trough is maintained level in all positions because of the parallelogram arrangement.

The flat bottom of the trough thus forms an excellent seal with a large contact area against the fibrous material being carried by the belt. A fiat surface area of about 10 square feet is found to be suitable for many available dryers; The sealing ability is not affected as much by the contact area per so as it is by the length (thickness) of the seal along the direction the belt-travels. This length coupled with the density of the fiber determines the ability of the seal to withstand a given pressure differential without blowing. -A seal having a 14 inch length (with an 8 foot width) is found suitable. However, a wide range of lengths is suitable, preferably from about 2-3 inches up to about 5-10 feetsThe limitations of practical construction and the size of the dryer must be considered.

The curved smooth surfaces of the sides of the trough contribute to the retardation of the build-up of contamination (e.g., entangled fiber masses at the seal). A

radius of curvature of about 6 inches is found to be suitable to preclude such formation. However, a wide range of curvatures are suitable, preferably, a radius of curvation from about 1-2 inches to about 2-3 feet. Contamination is also reduced due to the fact that seal is enclosed and cannot fill with staple. Another contributing feature is the location of the hinges at the top of the sides of the seal, high enough above the fiber, to prevent build-up of contamination at these points.

The trough and rectangular supporting members are made sufliciently wide to fit within the housing with relatively small clearance. Preferably, strips of flexible material, as previously shown, are also mounted at each end of the trough and supporting members to reduce the clearance and form a more perfect seal.

The improved seal provided by the inveniton is generally used both at the entrance to and at the exit from the dryer. However, the seal may be used at either end alone. The dryer may also be divided into compartments, and seals may be employed between adjoining compartments.

In commercial operation, dryers provided with the seals of the invention as described above have been found to operate at high efficiency in drying moist staple fibers of acrylonitrile polymer. Loss of heat owing to leakage of heated air is minimized, and the occurrence of fibers blown out by gusts of air at the entrance and exit is at a very low level. Use of this type of seal results in very little contamination of the product with discolored fibers or entangled masses of fibers attributable to the seals.

While the preferred embodiment of the invention has been shown and described, it is to be understood that changes and variations may be made without departing from the spirit and scope of the invention.

What is claimed is:

1. In an apparatus for drying fibrous materials comprising an elongated housing having an inlet and an outlet opening for said fibrous materials a continuous perforated belt mounted therein for carrying said fibrous materials through said housing, means for introducing a gas into said housing, means for heating said gas; and means for passing the heated gas through the said perforated belt and removing said passed gas from said housing; the improvement which comprises:

(1) a seal in at least one of said openings of said housing, said seal comprising a trough extending substantially across the width of said openings, said trough having enclosed ends parallel to the sides of said belt, said trough having a flat bottom curving upwardly to form curved front and rear sides perpendicular to the sides of said belt, and

(2) suspending means connected to said trough for allowing the movement of said trough towards and away from said belt while simultaneously maintaining said flat bottom of said trough substantially parallel to the face of said belt wherein said suspending means comprises two parallel rectangular members of substantially equal size extending substantially across the width of said opening, one edge of each of said rectangular members being attached by hinges to one of said sides of said trough, the opposite parallel edge of each of said rectangular members being attached by hinges to said housing, all of said hinges being parallel to the face of said belt, and perpendicular to the sides of said belt.

2. The apparatus of claim 1 wherein said seal is in said inlet of said housing.

3. The apparatus of claim 1 wherein said seal is in said outlet of said housing.

4. The apparatus of claim 1 having two or more of said seals.

5. The apparatus of claim 2 having two seals, one of said seals in said inlet of said housing, and the other of said seals in said outlet of said housing.

6. The apparatus of claim 1 further comprising a means 3,403,457 5 6 to prevent said flat bottom of said trough from approach- References Cited ing closer than a predetermined minimum distance from UNITED STATES PATENTS the surface of said belt.

7. The apparatus of claim 1 further comprising strips 8635830 8/1907 Ashley et 34216 of flexible material afiixed to the edges of said flat bot- 5 1,863,687 6/1932 Cramer 263-8 tom, said front sides and said rear sides of said trough 119411560 1/1934 Lee and the non-hinged edges of said rectangular supporting 3,130,079 4/1964 Meistermember; said strips of sufficient thickness to slidably contact the Walls of said opening of Said housing FREDERICK L. MATTESON, JR., Primary Exammer.

8. The apparatus of claim 7 wherein said flexible ma- 10 H. B. RAMEY, Assistant Examiner. terial is polytetrafiuoroethylene film. 

